Place pictures/graphics inside the actual day space?

"Day Pictures" are available on many but not all templates.
Each "Day Picture" is anchored and sized to its date.

"Day Pictures" can be selected by clicking "Day Pictures" on the "Pictures" or "Day Labels" menu. If "Day Pictures" is not visible then "Day Pictures" are not available for that template. Try selecting a different template - "Day Pictures" are generally available on templates with grids.

"Day Pictures" are not individually sizeable.
However you can select to have "Large" or standard "Day Pictures" via the "Day Pictures" menu.